a) Field of the Invention
The present invention relates to a technique for estimating a concentration of a vaporized fuel purged into an intake air system of an internal combustion engine in which a vaporized fuel processor is installed and a combustion condition is transferred between a lean air-fuel mixture ratio combustion and a stoichiometric air-fuel mixture ratio combustion.
b) Description of the Related Art
A Japanese Patent Application First Publication No. Heisei 7-42588 published on Feb. 10, 1995 exemplifies a previously proposed vaporized fuel processor for an internal combustion engine which is constituted by a canistor for adsorbing a vaporized fuel onto an activated carbon thereof and a purge control valve interposed in a purge passage of the vaporized fuel linked from the canistor to an intake air system of the engine for controlling a purge quantity of the vaporized fuel.
It is necessary to correct a fuel supply (injection) quantity according to the concentration of the vaporized fuel in the internal combustion engine having the vaporized fuel processor according to the concentration of the vaporized fuel.
An oxygen concentration sensor is installed in an exhaust gas passage of the engine for detecting a rich or lean exhaust gas air-fuel mixture ratio.
In the engine in which the air-fuel mixture ratio is feedback controlled so that the air-fuel mixture ratio approaches to the stoichiometric air-fuel mixture ratio, the above-described correction can be achieved by the air-fuel mixture ratio feedback control.